Word. Check out the Twilight armor enhancement from the Book of Exalted Deeds. Armor so enchanted has arcane spell failure reduce by 10%. And it is only a +1 bonus?!?
I actually found the answer to my own question yesterday. So for those of you interested, fey made (DMG II) padded, +500 reduces arcane spell failure by 5% which is all padded has. It does some other things too, but the key is armour that can be enchanted with no arcane spell failure.